The present invention relates to a crash can which is made of aluminum-alloy casting for a vehicle.
Vehicles are equipped with an impact absorption device to ensure the safety of passengers or reduce damages of a vehicle body in a vehicle collision against another vehicle or any obstacle, such as a building, due to driving mistakes. A crash can (box) is known as a representative impact absorption device, which is provided between a bumper reinforcement provided inside a bumper of the vehicle and an end portion of a side frame of the vehicle body.
The above-described crash can, which is generally made of steel, crashes in a vehicle longitudinally direction in bellows shape with buckling deformation in a vehicle frontal collision or a vehicle offset collision, and thereby absorbs a collision energy. The conventional crash can made of steel is formed by a pair of inside and outside members which have a U-shaped section, respectively, and connected to each other so as to provide a hollow tube shape. It is also known that the closed cross section of this crash can is formed in a cross shape or a tumbler shape, or it is formed to have beads at its inside wall face and its outside wall face. US patent application publication No. 2010/066124, for example, discloses the crash can made of steel and having the closed cross section formed in the cross shape, in which the concave portion provided at the front end face of the crash can engages with the convex portion having the U-shaped section which is formed at the rear face of the bumper beam to extend in the vehicle width direction.
It is also known that the crash can is made of aluminum alloy. Japanese Patent Laid-Open Publication No. 2002-39245, for example, discloses the tube crash can made of aluminum-alloy casting, in which the wall thickness of the crash can changes continuously or partially in its axial direction. Further, Japanese Patent Laid-Open Publication No. 2002-12165 discloses the crash can made of aluminum-alloy extrusion having the hollow rectangular section, in which the wall face of the crash can outwardly projects to provide the convex portion which extends in the axial direction and have the U-shaped section.
Further, another structure of the crash can which is disclosed in US patent application publication No. 2010/0032970 is also known.
Herein, the crash can made of aluminum alloy may be advantageous in providing a lightweight vehicle body, compared to the one made of steel, despite its wall thickness being relatively thicker to ensure the proper strength. However, in the case of the crash can made of aluminum-alloy extrusion, the same sectional shape basically extends over a whole length of the crash can in the axial direction. Accordingly, it may be difficult to change the sectional shape of the crash can made of aluminum-alloy extrusion in the axial direction in order to effectively obtain the impact absorption function or provide connecting flanges at both ends. Meanwhile, in the case of the crash can made of aluminum-alloy casting disclosed in the above-described second patent publication, while the wall thickness of the tube portion may be possibly changed or the flanges may be possibly provided, it has been desired to obtain the further effective impact-absorption function.
That is, when the collision load is added to the crash can, the crash can resists against the collision load, so that the load received by the vehicle body may increase until the buckling deformation occurs initially. Then, the load may decrease in accordance with the occurrence of the buckling deformation. Thus, a so-called initial peak may occur. After the crashing of the crash can caused by this initial buckling deformation, the crash can may not provide any effective absorption effect of the collision energy. Consequently, the damages received by the vehicle body and the impact received by passengers may become improperly large.
Even in a case in which the crashing of the crash can is not caused by the initial buckling deformation, the load received by the vehicle body may increase until the next buckling deformation occurs. Accordingly, if the subsequent buckling deformations do not happen properly continuously after the initial buckling deformation, the effective absorption of the collision energy may not be achieved, so that the impact received by the vehicle body may be improperly large.